Re: [exim] Implementation of SPF - flaw?

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Szerző: Richard James Salts
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Címzett: exim-users
Tárgy: Re: [exim] Implementation of SPF - flaw?


On 25 September 2017 18:26:27 CEST, Hardy <bulk@???> wrote:
>On 25.09.2017 14:45, Heiko Schlittermann via Exim-users wrote:
>> Hi,
>>
>> Hardy <bulk@???> (Mo 25 Sep 2017 09:17:34 CEST):
>>> Hi,
>>>> and clearly does not include localhost. So passing messags from
>>>> localhost might be a feature of SPF in general or of the
>implementation
>>>> in Exim.
>>>
>>> I wouldn't think localhost is handled special by SPF, but usually
>(in
>>> standard- and example configs) you have a very early rule ACCEPTing
>existing
>>> local users, before it does any "expensive" (netwise: DNS lookup
>etc.)
>>> actions. In this case your SPF is not even tested, which is the aim
>of this
>>> rule. You wouldn't want to greylist internal addresses either, would
>you?
>>
>> The debug output of my test session from localhost to localhost shows
>> that SPF was in use and gave 'pass' to localhost (with some note
>about
>> "localhost is always allowed")
>>
>> The string "localhost is always allowed." can be found in libspf2.a
>
>So this is wanted by exim! I did not check what SPF specs say about it,
>
>but this would mean, my local users CAN forge sender addresses?! Does
>this make sense?!


There are other acl conditions you can use to enforce the authenticated user being authorized to use the envelope sender or optionally the from/sender header. These would be with the generic condition modifier and expansions based on your local policy. They could be put in an smtp acl after mail or the non-smtp acl. If your policy is very simple then control = submission may be sufficient.

SPF is not a very good way of controlling policy between an MUA and submission service.

>
>RFC
>Hardy
>
>
>
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